Measuring device comprising a hall sensor and method for the pruduction thereof

ABSTRACT

The invention relates to a measuring device comprising a hall sensor, particularly for measuring devices, which is characterized by the fact that the hall sensor is arranged in a centrally and axially movable manner in a magnet pipe. Each half of said magnet pipe is transverse-magnetized with opposite polarity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/EP03/04161, filed Apr. 22, 2003. This application claims the benefitof German Patent Application 102 19 473.4, filed Apr. 30, 2002. Thedisclosure of the above application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a measuring device with a Hall sensor,particularly for displacement measurements, and to a method forfabricating the measuring device.

BACKGROUND OF THE INVENTION

It is known to use Hall sensors for measuring various parameters. Suchsensors are used, for example, for measuring magnetic fields, wattage inhigh-voltage power lines, for contactless control and regulation ofmotion, and many other uses. The measurement of motion, however, ispossible only for very short motion paths of only a few millimeters.

SUMMARY OF THE INVENTION

The object of the invention is to provide a measuring device with a Hallsensor to be used, in particular, for a displacement measurement wherebylonger paths than before can be measured with accuracy.

Another object is to provide a method for fabricating the measuringdevice.

According to the invention, in a measuring device with a Hall sensor,particularly for a displacement measurement, this objective is reachedby disposing the Hall sensor in a magnetic tube centrally so that it canbe moved axially. Each half of the magnetic tube is cross-magnetizedwith opposite polarity. Tests have shown that such a measuring deviceprovides very accurate measurements over a considerably longer pathlength than previous measuring devices with Hall sensors. For example,with a magnetic tube length of 20 mm, an approximately linear rangeuseful for the measurement having a length of about 14 mm was achieved.

In designing the measuring device, it is important that the Hall sensorbe kept in an axially displaceable support, or that it be displacedaxially in a support in a manner such that rotary motions of the Hallsensor relative to the magnetic tube are not possible.

The novel Hall sensor is of simple configuration and is suitable formeasurements over long paths. It is not subject to disturbances and isvirtually linear. Moreover, it does not require external electronicevaluation circuits. The Hall sensor is moved centrally in the magnetictube, wherein each half of the tube is cross-magnetized with oppositepolarity. The flux density is highest at a distance of a few millimetersfrom the poles. In the center of the magnetic tube, the flux density isnil and changes its direction.

Compensation of the temperature dependence can be achieved in a simplemanner by suitably pairing the Hall sensor with the material of whichthe magnet is made so that the temperature variations of the twomaterials compensate each other.

The fabrication of Hall sensors is in itself known. Different methodscan be used to produce the novel magnetic tube for the measuring device.An advantageous method consists of cross-magnetizing a tube made of amagnetizable material in a diametrically opposite manner so that, in theupper part of the tube, one half of the tube is magnetized as themagnetic north pole and the other half of the tube is magnetized as themagnetic south pole. In the bottom part of the tube, the procedure isreversed. That is one half of the tube is magnetized as the magneticsouth pole and the other half is magnetized as the magnetic north pole.

A very simple method for fabricating the magnetic tube for the measuringdevice consists of through-magnetizing a tube of magnetizable materialperpendicularly to its axis so that one half of the tube is magnetizedas the magnetic north pole and the other half of the tube as themagnetic south pole. The tube is then severed across its axis, and oneof the parts of the tube is turned 180° relative to the other part ofthe tube. In this manner are obtained the diametrically opposite northand south poles of the magnetic tube for the measuring device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail with the aid ofthe practical examples represented in the drawings, in which

FIG. 1 and FIG. 2 show a top view and a longitudinal sectional view ofthe configuration principle of the measuring device;

FIG. 3 shows a diagram of a measuring signal recorded in gauss againstthe measuring path;

FIG. 4 shows the procedure for diametrically oppositethrough-magnetization; and

FIG. 5 shows the use of the measuring device in a pneumatic adjustmentunit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a configuration of a measuring device 1 according to thepresent invention. The measuring device 1 consists of a magnetic tube 2with a north pole side 3 and a south pole side 4, as well as a Hallsensor 5 disposed centrally in the magnetic tube 2.

As can be seen from FIG. 2, the magnetic tube 2 is configured so that,as seen in the longitudinal direction, it is divided into two halves.One half 6 is configured with the north pole on the left side and thesouth pole 4 on the right side, and the other half 7 of magnetic tube 2is configured in the reverse manner. That is, the north pole 3 islocated on the right side and south pole 4 on the left side of themagnetic tube 2. As indicated by double arrow 8, in the magnetic tube 2,the Hall sensor 5 can be moved back and forth in the axial direction.For this purpose, there is provided a support, not shown in detail,which permits axial movement of the Hall sensor 5, but prevents the Hallsensor 5 from rotating relative to the magnetic tube 2.

FIG. 3 shows the diagram of a performed test in gauss against the pathlength. For a measuring device with a magnetic tube of 20-mm length, ausable, nearly linear range of about 14 mm was obtained. Measuring line10 was obtained by use of a Hall sensor 5 disposed in the middle of themagnetic tube 2, whereas measuring line 20 was obtained with a Hallsensor 5 disposed in the vicinity of the inner wall of the magnetic tube2. The outer diameter of the magnetic tube was 14 mm and the innerdiameter of the magnetic tube was 8 mm. For both measuring lines 10 and20, a range 15 is approximately linear and may be viewed as useful.

FIG. 4 shows a side view of the magnetic tube 2 used for themeasurements. The height of the tube was H=24 mm, the inner diameterDE=8 mm, and the outer diameter DA=14 mm. The upper half 6 of tube 2shown in the drawing was through-magnetized from left to right asindicated by arrow 11, whereas the lower half 7 of magnetic tube 2 wasthrough-magnetized in the opposite direction as indicated by arrow 12.This diametrically opposite through-magnetization of magnetic tube 2afforded the arrangement of magnetic poles 3 and 4 shown in FIG. 2.

FIG. 5 shows a practical example of the application of the novelmeasuring device 1. Measuring device 1 is disposed centrally in a vacuumadjustment unit used in the motor vehicle field. The configuration ofmagnetic tube 2 is that of the magnetic tube represented in FIGS. 1 and2. Hall sensor 5 is disposed centrally in the middle of magnetic tube 2.The entire measuring device 1 is disposed within a vacuum chamber 31 ofan adjusting unit 30. By means of the measuring device 1, the positionof a support 32 relative to its zero position can be measured andtransmitted to the electronic system of the engine.

1. A measuring device having a Hall sensor, for displacementmeasurements, wherein the Hall sensor is disposed centrally and in anaxially movable manner in a magnetic tube each half of said magnetictube being cross-magnetized with opposite polarity.
 2. The measuringdevice according to claim 1, wherein the Hall sensor is held in asupport in an axially displaceable manner, said support preventing arotational movement of the Hall sensor relative to the magnetic tube. 3.A method for fabricating a magnetic tube for the measuring deviceaccording to claim 1 wherein a tube made of a magnetizable material iscross-magnetized in a diametrically opposite manner so that one half ofthe tube is magnetized as a magnetic north pole and the other half ofthe tube as a magnetic south pole, and that in the opposite directionanother half of the tube is provided with a magnetic north pole and amagnetic south pole.
 4. A method for fabricating a magnetic tube for themeasuring device according to claim 1 comprising: through-magnetizing atube made of magnetizable material in a direction of its axis so thatone half of the tube is magnetized as a magnetic north pole and anotherhalf of the tube is magnetized as a magnetic south pole; and severingthe tube in its center crosswise to its axis; and rotating one part ofthe tube 180° relative to the other part of the tube.